1. Field of the Invention
This invention relates to a thin film transistor, and more particularly, to a method for fabricating a thin film transistor, which prevents damage to an active layer, by forming a transparent conductive material on the active layer and forming the pixel before forming the ohmic conductive layer. The transparent conductive material serves as an etch stopper when removing an ohmic contact layer positioned between a source and a drain electrode.
2. Discussion of the Related Art
A conventional process for fabricating a thin film transistor is to be explained hereinafter, with reference to FIGS. 1(a)-(f) of the attached drawings.
As shown in FIG. 1(a), gate electrodes 12a and 12b are formed and spaced at a fixed interval on a transparent insulation substrate 11. Then, as shown in FIG. 1(b), a gate insulation film 13 is formed on the gate electrodes 12a and 12b, as well as over the entire exposed surface of the transparent insulation substrate 11.
An active layer 14, having a fixed lateral width, is then formed on a surface of the gate insulation film 13 at a part overlying the upper side of a first gate electrode 12a.
As shown in FIG. 1(c), a pixel 15 is formed on a surface of the gate insulation film 13 at a part overlaying the gate electrode 12b in a vertical direction and a side extending laterally toward the active layer 14 leaving space between the active layer 14 and pixel 15. An example of the material of the pixel 15, is indium tin oxide (ITO).
As shown in FIG. 1(d), by forming high density ohmic contact n conductive material (hereinafter called `n+` layer) on the exposed surface of the transparent insulation substrate 11, the active layer 14, and on the pixel 15, and carrying out patterning of the formed n+ layer, an ohmic contact n+ layer pattern 16 is formed to cover the surface of the active layer 14, the surface of the space between the active layer 14 and pixel 15, and part of the surface of the pixel 15.
Then, by depositing electrode metal on the exposed surface, and carrying out patterning of the deposited metal, a source electrode 17 is formed on one part of the surface of the active layer 14 and a drain electrode 18 is formed on the surface of the other side of the active layer 14. The drain electrode extends to a portion of the surface of the pixel 15 and a space is provided between the source electrode 17 and the drain electrode 18.
As shown in FIG. 1(e), after removing the part of the ohmic contact n+ layer pattern, which overlies the upper side of the active layer 14 positioned between the source and the drain electrodes 17 and 18, as shown in FIG. 1(f), a protection insulation film 19 is formed over the entire exposed surface.
This conventional process is liable to damage the active layer 14 because of the large amount of etching of the ohmic contact n+ layer, which is required for removing the exposed ohmic contact n+ layer pattern, from above the active layer 14 after the source and the drain electrode 17 and 18 are formed.